مدل‌سازی آزمایشگاهی برهم‌کنش گسل‌ها در تکامل ساختاری تاقدیس‌های رگ سفید و تنگو (جنوب غرب ایران)

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه زمین‌شناسی، دانشکده علوم، دانشگاه بیرجند، بیرجند، ایران

2 گروه زمین شناسی، دانشکده علوم، دانشگاه بیرجند، بیرجند، ایران

چکیده

در فروبار دزفول جنوبی با توجه به توالی فاز­های دگرشکلی زاگرس و رخداد وارونگی تکتونیکی در گسل­ راندگی رگ سفید و همچنین تجدید فعالیت گسل­ پی سنگی هندیجان، بر هم­کنش عمودی بین گسل­ها در پیش بوم زاگرس اتفاق افتاده است؛ که این اثر متقابل تاثیراتی مهم بر الگوی ساختاری و تشکیل تاقدیس­های رگ سفید و تنگو دارد. فاز چین خوردگی اصلی در پیش بوم زاگرس و در تاقدیس­ رگ سفید در پلیوسن رخ داده است. جهت مدل­سازی آزمایشگاهی تکامل تکتونیکی، با توجه به محاسبه میزان کوتاه­شدگی عمود بر بخش مرکزی تاقدیس رگ سفید، با اعمال فشردگی به میزان 16 درصد و با حرکت فک­های متحرک دستگاه برش با سرعت ثابت، وارونگی تکتونیکی و تبدیل حرکت از کشش به راندگی در گسل رگ سفید سبب می­شود توالی لایه­ها دگرشکل شوند و چین خوردگی وابسته به گسل در تاقدیس رگ سفید تشکیل گردد. با ورود جبهه دگرشکلی زاگرس به پیش بوم منطقه کوهزایی در پلیوسن، علاوه بر برخاستگی تاقدیس تنگو در راس گسل هندیجان، محور تاقدیس رگ سفید به علت حرکت امتداد لغز راستگرد در گسل هندیجان، به میزان 30 درجه به صورت ساعتگرد می­چرخد. مدل­سازی ما نشان می­دهد که دلیل طول موج بیشتر بخش باختری تاقدیس رگ سفید به علت ضخامت زیاد لایه نمکی سازند گچساران و همچنین مقدار بالای نسبت  ضخامت لایه نامقاوم به لایه مقاوم است که در اثر واقع شدن بخش باختری تاقدیس رگ سفید در یک پهنه گسلی راستگرد و چرخش ساختاری حاصل از آن، پهن شدگی و افزایش طول موج تاقدیس تسهیل شده است.

کلیدواژه‌ها


عنوان مقاله [English]

Analog modeling of faults interaction in the structural evolution of the Rag Sefid and Tango anticlines (SW Iran(

نویسندگان [English]

  • Mehdi Yousefi 1
  • Seyed Morteza Moussavi 2
  • Mohammad Mehdi Khatib 2
1 Department of Geology, Faculty of Science, University of Birjand, Birjand, Iran
2 Department of Geology, Faculty of science, University of Birjand
چکیده [English]

Extended abstract
Introduction
The subduction systems are located in the continental collision phase. Due to the tectonic regime reversion from the tensile phase to the compressive phase and due to the reactivation of the normal and transverse basement faults, constitute folded belts that are in their tectonic evolution, have experienced multiple fault interactions. Therefore, based on the angle of post-collision shortening axis, relative to each of these old basement faults, their reactivation in the form of thrust or strike-slip components and their effects on the structural pattern of the folds, are justified. In the Zagros foreland, there are several fault lineaments with different trends and mechanisms. They have been reactivated during the collision phase of the Iranian and Arabian sheets. The present study tries to show the effect of the Zagros thrust faults and the Arabian strike slip faults interaction on the development and structural evolution of the Rag Sefid and Tango anticlines using analog modeling.
Materials and Methods
In order to model the interaction of basement faults in the South Dezful embayment, first, in accordance with the structural realities of the region, the topography of the basement is simulated using the cutting of wooden boards. The arrangement and cutting of the boards are according to the slope of the Rag Sefid thrust fault. First the wooden board is cut at an angle of 47 degrees. Also, considering that about one third of the Rag Sefid anticline has an axial curvature, and due to the slope of approximately 80 degrees at Hendijan fault, which is perpendicular to the Rag Sefid fault, the wooden board is cut into two unequal parts with an 80-degree slope. According to the interpretation of reflective seismic sections and drilled well data, the stratigraphic sequences detectable in the southern Dezful embayment are Aghajari, mobile Gachsaran formation and Middle Resistance Group between Asmari to Gadvan, respectively. Therefore, in order to model these stone units, clay with a thickness of 3 and 2 cm was used for upper and middle resistant units, respectively. Also, in order to simulate the Gachsaran moving formation, a combination of sifted rock powder and 3 cm thick engine oil is used at the beginning of modeling.
Results and discussion
The northwest-southeast trend of Rag Sefid anticline located in Zagros foredeep, has been raised due to the Zagros orogenic phase in the Pliocene. After the collision of the plates from the Late Eocene onwards, in addition to folding on the northwest-southeast faults, the north-south basement faults during the Late Cenozoic have been reactivated by the entry of the Zagros deformation front into the study area. The reactivation of these faults has caused changes in sedimentary cover, such as facies change and sediment thickness as well as changes along the axis of surface anticlines. Oblique convergence after collision between Iran and the Arabian Plate has shortened the succession of the Zagros basement; so that the northwest-southeast longitudinal faults that were extensional at the time of the rift formation are now basement thrusts in this belt. The north-south faults, which have trends similar to those of the north-south basement fault in the eastern Arabian Block, are reactivated as a result of this compression.
Conclusion
Due to the general compression trend of N22E in southwestern Iran and the trend of the southern part of the Hendijan fault (N20E), the small-scale fold at the Tango anticline located on the Hendijan fault is due to the parallelism of this transverse fault and the overall compression direction. In contrast to the Rag Sefid anticline, where the trend of the main fault is approximately perpendicular to the direction of total compression (N100), a clear fold with large structural dimensions is created in the Rag Sefid anticline. Our results show that with the entry of the Zagros deformation front into the foreland of the orogenic region in the Pliocene, in addition to the Tango anticline rising at the top of the Hendijan fault, the Rag Sefid anticline has rotated axially by 30 degrees clockwise due to the movement of the right-hand slip in the Hendijan fault. Our modeling shows that the reason for the higher wavelength of the western part of the Rag Sefid anticline is due to the high thickness of the salt layer and also the high value of the ratio number. Due to the location of the western part of the Rag Sefid anticline in a right-sided fault zone and the resulting structural rotation, the widening and increasing wavelength of the anticline is facilitated.

کلیدواژه‌ها [English]

  • Fault Interaction
  • Modeling
  • Rag Sefid Anticline
  • Hendijan Fault
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